This week's heatwave is only the beginning. The mercury may not have pipped the all-time record on Wednesday, but it is only a matter of time. Maybe not next week and maybe not next month, but soon. And for the rest of our lives.

The planet is warming rapidly. Arctic ice is at record lows and the north pole could melt to open water sometime this century for the first time in some 40m years. The mighty West Antarctic ice sheet is creaking and dramatic changes are expected, from the Amazon rainforest to the Siberian permafrost. But what about the UK? What else does global warming have in store for our once green and pleasant land?

Peering into the future is a tricky business, especially for something as volatile as weather and climate. But scientists know a lot about how events will unfold. They use giant computer programs, evolved from those that make weather forecasts, to work out how the atmosphere will react to the blanket of carbon dioxide we humans are steadily wrapping around the planet. As we do, and as more of the sun's heat is unable to escape, the air and the sea warm. But that takes time, which means that whatever we do, our climate destiny is fixed for the next few decades.

Only now is the planet finally coming to terms with the carbon spewed into the atmosphere while the Beatles ruled the charts. And today's carbon pollution from cars, power-hungry plasma screen televisions and cheap flights will only wreak its havoc long after Coldplay and the Arctic Monkeys have faded into the distant past. That makes predictions over the next few decades pretty accurate. Beyond that, the picture is fuzzier but experts use various scenarios to bring it into focus, which differ depending on how quickly we switch from sources of energy that rely on carbon.

Here, we present a picture of what might happen in Britain over the next century if the world fails to take serious action, and global emissions continue to rise at about the same, or a slightly slower, rate. So what does it reveal? More good news than you may expect: British farmers may have something to smile about and the increased victims of heatstroke are more than compensated for by the thousands of vulnerable people saved from bitter winters. Summer fetes are less likely to be rained off and English wine could come in from the cold.

But if that is the good news, here comes the bad: floods, malaria, shark attacks, sweltering summers and worsening drought. Rainfall will decline in the summer and the increased deluges in winter will struggle to replenish thirsty reservoirs because much of the water will run off the baked ground. Rapid changes in temperature will confuse wildlife and a white Christmas will be a distant dream.

Outside the UK, of course, the situation will be more dire, with developing countries expected to be particularly badly hit by food shortages, flooding and disease. But Britain too could face a harsher fate - many scientists think climate change could leave the orderly, linear path plotted here and start to run out of control. The impact of global warming could yet surprise us.

What's in store if we don't act now

Temperature

2020s Temperatures in the UK are expected to rise about 0.4C each decade, meaning that average temperatures will be up by about a degree by the 2020s on current conditions. The degree of warming will reflect existing weather differences across the UK, so the north-west of the country will warm the least. The south-east will see the biggest rise - up to 1.5C higher than today on average.

2050s A thicker blanket of carbon dioxide wrapped around the planet means summers will be an average 3C hotterthan todayin the south-east andup to 1.5C warmerin the north of Scotland. Winters will be at least 1.5C warmer across the country, with the effects felt most strongly at night.

2080s Virtually every summer in England and Wales could be warmer than during the 1995 heatwave. Average temperatures across the UK will reach 3C higher than today, peaking at 5C higher in the south-east. Night will offer little respite. Each 1C of warming takes an extra hour to dissipate, so the south could feel as warm at midnight on summer evenings as it does at 7pm today.

Weather

2020s Warmer winters means less snowfall across the UK. Changes in rainfall are not likely to be straightforward, but they can be summarised as drier summers and wetter winters. Overall, there will be about 5% less rainfall than at present, peaking at 20% less in summer in the south-east. Winters across the UK will see about 10% more rain. Much of the increased winter rainfall could come in heavy downpours.

2050s Summers could be 25% drier across England, 10%-15% drier in Scotland. The east coast of the UK will bear the brunt of the extra winter rain, approaching 20% more than at present. Only the north-west of Scotland may not notice any difference, though the summers there will be marginally drier. Snow will be down 50% across lowland areas and up to a third less across higher regions. Relative humidity in the atmosphere will be down, producing about 10% fewer foggy mornings in winter.

2080s Summer rain on the south coast could be down to just half current levels, well over 40% down across the rest of England and about 30%down in Scotland. Winter rainfall in scattered eastern parts could peak at more than 30% above current levels, and is likely to fall in heavy bursts. On average the UK will see about 10% less rainfall. Snow in parts of the UK will be down. Winter gales caused by areas of low pressure could rise by 40% across the UK.

Sea level and flooding

2020s Contrary to popular belief, ice caps and glaciers do not need to melt to force up sea levels - warmer temperatures are enough because hotter water expands, and this will account for most of the rise over the next century. By the 2020s, the global sea level is expected to rise by about 6cm. Sea level rise across the UK will not be even because the bedrock we sit on tilts, with the south-east sinking and the north-west rising.

2050s Seas around most of England could be 30cm higher, with the rise in the north-west and Scotland not as severe. Scientists are reluctant to simply morph these changes on to contour maps, because it is unrealistic to expect no action to be taken to defend valuable land. In other places, the sea could be allowed to advance in a managed retreat. The risk of flooding due to storm surges will increase. Vulnerable areas will be under water more often, and places with no history of floods could be threatened.

2080s Sea levels could be 70cm higherat the southern end of the UK and some 50cm up along the north-western coast. An estimated 2 million extra people will be at risk of flooding and there will be a 17-fold increase in the flood risk along the east coast. London could face a £25bn clean-up bill after a freak storm surge that would overwhelm the Thames barrier. Higher sea levels mean deeper coastal water and more powerful waves battering the shore, wearing down defences and eroding soil.

Public health

2020s As the thousands of extra deaths across Europe during the 2003 heatwave demonstrated, hotter summers are a killer. The Department of Health predicts about 1,000 more heat-related deaths each year by the 2020s, mainly among sick and older people. Warmer conditions also help bugs to thrive - expect 4,000 extra cases of food poisoning. But warmer winters are expected to bring about 14,000 fewer cold-related deaths.

2050s Home-grown malaria could make an appearance as mosquitoes thrive in the new temperatures, but is unlikely to pose a major health risk. The hotter summers could kill up to 2,000 more people each year, but cold-related deaths in wintercould be down by 20,000. Food poisoning bugs will provoke an extra 9,000 serious cases each year. Increased exposure to ultra-violet radiation during warmer and cloudless summer days could cause 2,000 extra cases of cataracts each year and 30,000 more cases of skin cancer.

2080s Milder winters with little frost and snow could save 29,000 cold-related deaths each year. Some 2,800 more people could die due to soaring summer heat and food poisoning will bring down an extra 14,000 each year. The rise in winter gales is expected to increase hospital admissions of people struck by flying debris, or crushed by falling trees and collapsing buildings.

Agriculture

2020s Current levels of carbon dioxide in the atmosphere are below the optimum for photosynthesis, so rising carbon emissions could boost growth and yields. A longer growing season, with earlier plantings could also help farmers. But drier summers could hit grass production and, without irrigation, some parts of the country could become too dry to grow existing crops.

2050s Yields of winter wheat could rise by 15%-25% and sugar beet by 16% in the south-west and 23% in the north-west, though these gains could be threatened by pests and weeds that might flourish in the new climate. Oilseed rape may struggle, but the range of sunflowers and maize could spread northwards to take its place. Livestock farmers in the south may be forced to grow forage maize to feed their animals, as water shortages bite and autumn silage production falters.

2080s English winegrowers could be harvesting French grape varieties on the slopes of the Lake District. Peaches and winter lupins may be common on the south coast.

Flora

2020s The range of many plants and animals will shift northwards, as they follow their desired temperature. The precise changes are difficult to predict because some species will struggle to move quickly enough. Beech trees could find it too warm on the south coast by the 2020s, but if they are to flourish in more suitable areas further north, they could need humans to plant their saplings.

2050sAsh trees are expected to disappear from southern counties such as Hampshire. The bluebell will lose out in Snowdonia, where shrub and grassland will be replaced by bog, fen and swampland. Bracken and gorse could spread to higher slopes. The milder winters will play havoc for fruit such as blackberries that require frost - the makers of Ribena, who boast of using only British berries, are already hunting for new varieties.

2080sLowland pine forests will start to die out and the lack of rain will hit grassland regions hard, particularly in the south.

Fauna

2020s Several species of butterfly could besqueezed from the warmer south but may find their natural path to cooler climes in the north blocked by a shortage of suitable habitat in the Midlands. The situation in the sea is simpler and tropical fish, octopus and squid will appear in the English Channel and southern waters in greater numbers as cold water species such as cod head away.

2050s Winter migrant birds such as the redshank could become more common. The hairy wood ant could overrun the Scottish highlands and the pied flycatcher will disappear from Wales. In the seas, populations of sand eels - small, silvery fish that spend much of their time buried in the seabed - could be disrupted, with knock-on problems for the seabirds that eat them.

2080s The south will be too warm for the nuthatch and birds such as the dotterel and the capercaillie could be driven to extinction in the UK. Great white sharks could be regular visitors to the coast, and discover an increased number of bathers enjoying the balmy climate.

People

2020sBritish holidays could boom, but increased visitor numbers will spell problems for footpaths in already overrun and eroded national parks such as the Lake District. So could heavier winter rainfall, especially with more walkers equipped and willing to go out in bad weather. Cafe culture in cities likeManchester might blossom, but will people be prepared to brave the urban summer heat?

2050sClimate refugees from increasingly arid and drought-struck southern Europe could swarm to our shores. So could displaced people from countries at increased risk of flooding such as Bangladesh. Existing public transport infrastructure such as the London Underground, designed and run without air conditioning, could become unbearably hot in the summer.

2080s Officials may be forced to rejig the school year, with July and August too hot for traditional summer holidays. Skiing holidays could once again be the preserve of the rich, with many current Alpine resorts below the new snow line. Our national characteristics could melt away in the heat - better weather may encourage British teenagers to spend more time outside and less in their bedrooms and garages making music. And with the weather invariably hot and dry, what will we talk about all of the time?